1. Field of the Invention
This invention relates to a method of and a system and a program for detecting an abnormal shadow in a radiation image, and more particularly to an improvement in detecting a prospective abnormal shadow.
2. Description of the Related Art
In the medical field, to find a diseased part of a patient or to observe a diseased part of a patient and diagnose progress of disease by reading a radiation image of the object (patient) has been a common operation. However, radiation image reading often depends upon experience and abilities of the reader and is not necessarily objective.
For example, it is necessary to find an abnormal shadow representing a growth and/or a micro calcification representative of a cancerous part in a mammogram (a radiation image of a breast) taken for the purpose of a breast cancer examination. However, depending on the reader, the abnormal shadow range cannot be properly detected. Accordingly, there has been a demand to properly detect an abnormal shadow including shadows of a growth and a micro calcification irrespective of the abilities of the reader.
In order to meet this demand, there have been proposed abnormal shadow detecting systems, for instance, in U.S. Pat. No. 5,761,334 in which a prospective abnormal shadow region in an image of an object is automatically detected by the use of a computer on the basis of image data representing the image.
In the abnormal shadow detecting system, a prospective abnormal shadow region is automatically detected by the use of an iris filter processing which is mainly suitable for detecting a growth shadow and/or a morphology filter which is mainly suitable for detecting a micro calcification shadow.
In order to improve prospective region detecting accuracy, there has been proposed, for instance, in Japanese Unexamined Patent Publication No. 2002-109510, a method of detecting a prospective abnormal shadow region in two stages where a characteristic value on the image is calculated for the prospective abnormal shadow regions detected by the technology described above and whether or not the prospective abnormal shadow region is of a malignant one is determined on the basis of the calculated characteristic value.
Recently, there have been proposed various methods of detecting a prospective abnormal shadow region in addition to the methods using the iris filter and a morphology filter. However, whether or not the prospective abnormal shadow region is of a malignant one is determined by the same method irrespective of the method of detecting a prospective abnormal shadow region.
Since the prospective abnormal shadow region has a characteristic which differs by the kind of detection used for detecting the prospective abnormal shadow region, the method where whether or not the prospective abnormal shadow region is of a malignant one is determined by the same method irrespective of the method of detecting a prospective abnormal shadow region cannot fully utilize the characteristic of the prospective abnormal shadow region, which can result in deterioration in abnormal shadow detecting performance.